The present invention relates to testing for various properties of ice samples and more particularly to testing for impact properties of a large ice mass such as an iceberg.
Offshore environments are becoming increasingly important as a food source and as an energy source. For example, as land based hydrocarbon fuel sources are exhausted, reliance on offshore sources for hydrocarbon fuel is enhanced. Design criteria for offshore facilities, such as an oil production or drilling platform include wave height, wind velocity etc. However, particularly in the north Atlantic, structural designs must include provision for impact by a solid mass such as an iceberg.
Many methods of testing ice have been developed under a variety of conditions. These types of tests may be performed in the field as well as in a laboratory cold room where the temperature may be controlled.
The types of impact tests that have previously been performed are those associated with crack propagation such as the Charpy impact test, penetration of a rigid indentor into or through the ice, a weight impacting a uniaxial specimen, or a rigid sphere dropped on a flat ice surface. Of these kinds of tests, the sphere dropped on a flat ice surface best represents the ice failure mechanism which will occur when an iceberg collides with an offshore structure. That is a blunt rigid body impacting a rather blunt large ice mass in which the ice becomes crushed at the area of contact and gets squeezed out between the two bodies.
Up until now this kind of testing has been done by transporting a large impact device to the location where ice is to be tested. Normally, these methods and apparatus are only suitable for impact testing a stable, immovable ice mass such as a frozen surface of a lake, river or other large body of water. Whenever the ice mass to be tested is unstable or movable, such as ice floating in water, impact testing is not meaningful.
In order for impact testing to be meaningful for offshore structures, either the ice or the impact device must be firmly positioned. A small ice mass floating in water is not satisfactorily positioned to absorb the force of an impact device. As a result, the ice mass will deflect away from the force imposed by the impact device and give little or no indication of the impact.
An iceberg, such as that found in the north Atlantic, may range up to one hundred million tons. Due to the temperature difference between ambient air and water, the portion of the iceberg above the surface of water will melt at a different rate from that below the surface. As such, the center of gravity of the iceberg will constantly shift causing the iceberg to roll in the water.